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I am planning on running my Phase II SOHC heads on the EJ257 I just picked up. From what I have read it seems the only thing the heads need to support near 400 to 500 hp is new valve springs.

Options I have found:

Cosworth springs sold by rallitek (I don't think they are the right height but rallitek lists them under 2.5l NA)

TWE springs, can't find a vendor that stocks them (Besides their website) Not much new (after 2005) info about them that I could find through searching.

Supertech springs and retainers, didn't see a vendor on here selling them but many websites seem too. I didn't find much info on these on the SOHC heads but it seems like they are used fairly often on wrx/sti DOHC heads

Ferrea doesn't list any springs that would work for the SOHC heads

Another question. I am going to run the motor as an N/A motor for quite a while until I get a turbo setup compiled for the car. It is going from 9.7:1 compression to right around 9.0:1 compression. Am I going to run into any lean/rich (I am guessing maybe a tad rich) conditions if I try to let the stock ECU control the fuel? I was guessing it would be able to compensate for this change but maybe I am wrong?

I found some info in the EJ257 FAQ thread that I missed. One of the posts talks about using the EJ257 on the stock ecu under vacuum. It seems like it should be fine. That thread is HERE.

I still have to choose valve springs. It seems that the correct installed height should be 35.5mm, which Supertech and TWE definitely offer. The Cosworth website says that their valve springs installed height is 36mm @ 62 lbs. The Supertechs installed are 35.5mm @ 70 lbs so it seems to me that extra half mil could be taken out by a little more pressure @ installed height while using the Cosworth springs.

The reason I don't just jump on the supertechs is I don't know how reliable importperformanceparts.net is. Has anyone ever used them?